Belt conveyors are commonly used to handle materials in many diverse fields ranging from mining and quarrying to food and feed production. The belt conveyors are typically used to transport materials from a first holding area such as a material handling vehicle's scoop or bucket, a hopper or a silo to a second holding area such as a mixing tank, a packaging area, a vehicle loading area or indeed to a different hopper or silo.
Frequently, the materials passing over the belt conveyor must be weighed. This enables the amount of material delivered to the second holding area to be carefully monitored which facilitates stock control. In some cases, accurately weighing the materials passing over a belt conveyor will facilitate the delivery of specified quantities of materials into a mixing vessel, for example, the amount of sand and aggregate delivered to a concrete mixing/delivery truck.
Belt conveyors typically comprise an endless belt led over a driven roller at one end of the belt conveyor and a following roller at the other end of the belt conveyor spaced apart from the driven roller. A plurality of idler rollers are provided intermediate the driven roller and the following roller to support the conveyor belt and the materials thereon and to limit the sag of the belt between the driven roller and the following roller. Generally speaking, the longer the span and/or the heavier the materials being supplied on the belt, the more idler rollers that are provided.
In order to weigh the materials passing over the belt conveyor, it is preferable to weigh the materials on the belt at a location spaced apart from either end of the belt conveyor. In other words, it is preferable not to take the weight measurement at or adjacent to either the driven roller or the following roller due to the sudden changes in loads often experienced at these locations. Therefore, it is generally accepted practice to measure the weight of materials passing over a belt conveyor at a point between the driven roller and the following roller. This ensures more consistent weighing of the materials.
In order to weigh the materials in this manner, it is common practice to disconnect an entire idler roller assembly from the frame of the conveyor, mount a sub frame having load cells thereon onto the conveyor frame and thereafter support the entire idler roller assembly on the load cells supported by the sub frame. One such system that has proven to be useful is that sold by Belt-Way Scales Inc., of Rock Falls, Ill., USA. Other commonly known belt scales are those described in detail in PCT Patent Publication No. WO2007/098465 in the name of New Enterprise, US Patent Publication No. US2007/074560 in the name of Dietrich, and UK Patent Publication No. GB2128345 in the name of Mitchell Cotts.
Although many of the known solutions for weighing materials on a belt conveyor are highly efficient, there are however some problems with the known solutions. First of all, the known systems are relatively time consuming to install. Typically, the idler roller assembly must be removed from the conveyor frame, holes must then be drilled into the conveyor belt frame, the sub-frame is then mounted on the belt conveyor frame before finally the idler roller assembly is mounted on the sub frame. Once in position, the next adjacent pair of idler rollers, one either side of the weighing idler roller, and in some cases two idler rollers either side of the weighing idler roller, must be shimmed so that the three (or in some cases five) idler rollers are substantially in line with each other to ensure accurate measurement. This is time consuming to perform during which time the conveyor belt will be out of operation perhaps resulting in lost revenue. Another problem with the known solutions is that by and large, the components and in particular the load cells are susceptible to damage caused by materials falling from the belt and accuracy of measurement may be diminished by build-up of materials on the load cells.
It is an object therefore of the present invention to overcome at least some of the problems with the known solutions.